First report of rubber circular leaf spot disease pathogen Colletotrichum siamense Prihastuti, L. Cai & K.D. Hyde in Cinnamomum zeylanicum blume in Sri Lanka

Abstract

innamomum zeylanicum, a member of the family Lauraceae, is commonly grown as an intercrop in Sri Lankan rubber plantations to provide additional income for growers. However, diseases affecting intercrops pose a potential threat to rubber, as pathogens may spread between host species and increase economic losses. This study aimed to identify potential pathogens associated with diseased cinnamon leaves. Leaf samples collected from lesion margins were surface sterilized and cultured on Potato Dextrose Agar (PDA). Distinct fungal colonies were sub-cultured, and ten morphologically different isolates were purified through single-spore isolation. Pathogenicity tests were conducted according to standard procedures to establish Koch’s postulates. The most virulent isolate was selected for morphological characterization and molecular identification using bi-directional sequencing of the ITS gene region. The pathogen was identified as Colletotrichum siamense (WDCM accession number RRISL87), which showed high pathogenicity on both cinnamon and rubber leaves. This study represents the first report of C. siamense infecting cinnamon and highlights the importance of further pathogen identification to strengthen quarantine measures and improve disease management strategies.